Worried baby will be too small

I’m almost 20 weeks pregnant and have my anatomy scan in a few days.

I was a normal weight before getting pregnant (5’9” and 148 pounds) but I was so sick the first trimester I dropped to 135 pounds. I have gained a few pounds back so am at 139. I feel like I’m eating, but I still havent had a huge appetite especially for protein. Anyone else lost weight and everything was okay? I’m worried they will tell me at anatomy scan that baby is too small or not growing at a healthy rate.

Is it possible to have a big baby even if I’m not gaining?